Recently, multilayer optical recording media utilizing two-photon absorbing materials are proposed to increase the density of recorded information in the optical recording media. To decrease crosstalk in the multilayer optical recording media, a structure in which a non-recording layer is disposed between recording layers is proposed (for example, refer to Patent References 1 and 2). However, the multilayer optical recording media having the laminate structure described above are, in general, obtained by forming and laminating each layer by the spin coating process, and a problem arises in that maintaining the precision of the thickness of the film is difficult since the error of the thickness increases as the lamination is repeated.
As a method for overcoming the problem, for example, a process in which a sheet of a thin film of a non-recording recording layer constituted with a pressure sensitive adhesive is attached to a substrate plate, a recording layer having a smaller thickness is formed on the non-recording layer by a coating process such as a spin coating process or a knife coating process, and these procedures are repeated to form the desired number of laminated layers, may be conducted. In this case, in general, a barrier layer is formed between the pressure sensitive adhesive layer and the optical recording layer since resistance of the pressure sensitive adhesive to solvents is poor. The two-photon absorbing material used for the recording layer is frequently a low molecular compound, and the strength of a sheet is insufficient when the sheet is formed from the material. To overcome this problem, in general, a binder polymer exhibiting poor two-photon absorbing property is mixed as the matrix. However, this method decreases the recording sensitivity as the recording layer.
As another process, a process in which a sheet of a thin film of a recording layer constituted with a two-photon absorbing material and a sheet of a thin film of a non-recording layer constituted with a pressure sensitive adhesive are laminated, is proposed (for example, refer to Patent Reference 3). In accordance with the process using the above sheet, several layers can be laminated to the substrate plate in a single step by preparing a unit in which several sheets of a thin film of a recording layer and several sheets of a thin film of a non recording layer are laminated, and production of a multilayer optical recording medium can be facilitated.
[Patent Reference 1] Japanese Patent Application Laid-Open No. Heisei 11(1999)-250496
[Patent Reference 2] Japanese Patent Application Laid-Open No. 2000-67464
[Patent Reference 3] Japanese Patent Application Laid-Open No. 2005-209328